1. Field of the Invention
The present invention relates to devices for executing a preceding vehicle following driving control, and in particular relates to devices capable of reducing fuel consumption of motor vehicles.
2. Description of the Related Art
There are known devices capable of executing a preceding vehicle following driving control. Such devices assist an own vehicle to drive on a lane following a preceding vehicle (or a forward vehicle). Through the description, the preceding vehicle is defined as one which is running in front of the own vehicle on the same lane.
For example, a first conventional patent document, Japanese patent No. JP 3889131, discloses an operation unit mounted around the steering wheel of an own vehicle. The driver of the own vehicle operates the operation unit during an auto-cruise driving mode in order to adjust a deceleration speed of the own vehicle and to adjust a vehicle distance between the own vehicle and a preceding vehicle. The preceding vehicle is running on the same lane of a road in front of the own vehicle.
A second conventional patent document, Japanese patent laid open publication No. JP 2009-113763 discloses a device which detects whether or not a current driving mode of the own vehicle is a usual following driving mode or a following driving mode with fuel consumption reduction. When the detection result indicates the following driving mode with fuel consumption reduction, the device controls the own vehicle so that the own vehicle follows up at an acceleration speed which is smaller than an acceleration speed of the usual following driving mode.
A third conventional patent document, Japanese patent laid open publication No. 2008-280017, discloses a conventional preceding vehicle following driving control which using a compensated evaluation index value KdB_c. This compensated evaluation index value KdB_c is an index which is obtained by compensating an evaluation index value KdB in consideration with a vehicle speed of a preceding vehicle which is running in front of the own vehicle on the same lane of a road. That is, the evaluation index value KdB is an index capable of indicating an area change rate of an object per unit time which is observed by the driver of the own vehicle. That is, the object is present in front of the own vehicle and now seen by the driver of the own vehicle. For example, such an object is a preceding vehicle which is running in front of the own vehicle on the same lane of a road. The evaluation index value KdB and the compensated evaluation index value KdB_c can be expressed by the following equations (1) and (2).
In the equations (1) and (2), reference character D designates a vehicle distance between the own vehicle and a preceding vehicle, Vr indicates a relative speed of a current speed of the own vehicle to a vehicle speed of the preceding vehicle, a indicates a multiplier, and p indicates a vehicle speed of the preceding vehicle.
                    KdB        =                  10          ×                                    log              ⁡                              (                                                                        4                    ×                                          10                      7                                        ×                                          Vr                                              D                        3                                                                                                              )                                      .                                              (        1        )                                KdB_c        =                  10          ×          log          ⁢                                    {                                                                4                  ×                                      10                    7                                    ×                                                            Vr                      -                      aVp                                                              D                                              3                        ⁢                                                                                                                                                                                                  }                        .                                              (        2        )            
In the above equations (1) and (2), the more the absolute value of the relative speed Vr when the own vehicle approaches the preceding vehicle is increased, the more the compensated evaluation index value KdB_c is increased. Further, the more the vehicle speed Vp of the preceding vehicle is increased, the more the compensated evaluation index value KdB_c is decreased. Still further, the more the vehicle distance D between the own vehicle and the preceding vehicle is decreased, the more the compensated evaluation index value KdB_c is increased.
Because the vehicle distance D is a cube of D in the equations (2), the more the vehicle distance D is decreased, the more a slope of increasing the compensated evaluation index value KdB_c to the change in decreasing the vehicle distance D is increased.
The conventional device and method disclosed in the third conventional patent document executes the following driving control of the own vehicle on the basis of the compensated evaluation index value KdB_c, it is possible for the driver of the own vehicle to comfortably follow the preceding vehicle.
However, the device, disclosed in the first conventional patent document, decreases the current vehicle speed of the own vehicle to a vehicle speed of another vehicle on the basis of a deceleration speed obtained by a control model when the current vehicle distance is decreased less than a preset vehicle distance when another vehicle cuts in between the preceding vehicle and the own vehicle or the vehicle speed of the preceding vehicle is decreased. This control makes it possible to maintain a safe vehicle distance between the own vehicle and the preceding vehicle or between the own vehicle and the other vehicle when the other vehicle cuts in between the own vehicle and the preceding vehicle, and the other vehicle becomes a new preceding vehicle on the same lane or when the preceding vehicle is decelerated.
However, when the other vehicle or the preceding vehicle is accelerated, the vehicle distance between the own vehicle and the preceding vehicle is increased, and the device instructs the own vehicle to accelerate its driving speed. This consumes fuel and decreases the fuel consumption. Through the specification, the “fuel consumption” can be adapted to electric vehicles which are propelled by electric motor(s), using electrical energy stored in batteries or another energy storage device.
Because the device disclosed in the second conventional patent document controls the vehicle speed of the own vehicle so that the vehicle distance between the own vehicle and the preceding vehicle is always kept at a constant distance, the device decelerates the vehicle speed of the own vehicle in order to maintain a constant vehicle distance between the own vehicle and the preceding vehicle when another vehicle cuts in between the own vehicle and the preceding vehicle or when the preceding vehicle decelerates. Accordingly, when the preceding vehicle or the other vehicle accelerates its vehicle speed and the vehicle distance between the own vehicle and the preceding vehicle is increased, the device also accelerates the current vehicle speed of the own vehicle. This control also increases the fuel consumption of the own vehicle because of executing acceleration and deceleration many times.
Still further, the device disclosed in the second conventional document can suppress the fuel consumption from being increased when the device selects the fuel-consumption reduction drive mode. However, this following driving control mode suppresses the own vehicle from being accelerated, and this control mode may deteriorate the following driving of the own vehicle to the preceding vehicle.
The device disclosed in the third conventional patent document detects the timing to accelerate or decelerate the vehicle speed of the own vehicle on the basis of the compensated evaluation index value KdB_c, as previously explained. However, the compensated evaluation index value KdB_c is also increased when the preceding vehicle decelerates its vehicle speed or when another vehicle cuts in between the own vehicle and the preceding vehicle, the device decelerates the own vehicle in order to decrease the compensated evaluation index value KdB_c. After this control, when the other vehicle or the preceding vehicle decelerates its vehicle speed, the device accelerates the own vehicle in order to increase the compensated evaluation index value KdB_c. As previously explained, the devices disclosed in the third conventional patent document, like the devices disclosed in the first and second conventional patent documents, deteriorate the fuel consumption because of executing frequently deceleration and acceleration of the own vehicle.